Renewable fuse



H I5 Attorney.

/6 Fred' G. Von HOOYWM Patented May 24, l1949 RENEWABLE FUSE Fred G. von Hoorn, Nichols, Conn., assignor to General Electric Company, a corporation of New York Application February 10, 1948, Serial No. 7,331 l f l The present invention relates to renewable electric fuses of the cartridge type.

It is an object of my invention to provide an improved fuse link assembly in a renewable fuse.

It is a further object of my invention to provide an improved securing means for thev fuse link in a renewable fuse.

More specifically, my object is to provide a washer for use between the fuse link and the head of its securing screw which shall accomplish the following purposes. It shall protect the operator from injury by slipping of his screw driver or other tool. It shall protect the head of the screw from damage from an arc developing when the Afuse blows. The washer shall provide a renewable arcing tip to receive the arc and thereby keep the arc away from the contact surface of washer and fuse link. If any welding between washer, link and terminal does occur,

the washer is to provide means for easy breaking y of such a weld with a usually available tool, such as a screw driver. The washer also shall facilitate renewing of the fuse link without turning the fuse link holder assembly upside down.

My invention will best be understood from the following description taken in connection with the accompanying drawing in which Fig. l is a longitudinal section through a renewable fuse casing showing my improved link securing means in elevation and Fig. 2 is yan enlarged section taken along the line 2-2 in Fig. 1.

My invention is applicable to a variety of renewable fuses in which the fuse link is held in position within the fuse enclosure by screws. I have illustrated my invention as applied to a conventional cartridge type fuse which I shall first briefly describe.

The fuse shown in Fig. 1 has an insulating casing l tted at the ends with metal ferrules 2 and 3 threaded inside the cartridge. The fuse link supporting element is shown as having knife blade contact terminals 4 and 5 joined by bar 8 of suitable insulating material. The bar 8. may be secured to the inner ends of the knife blade terminals in any suitable manner, for example, by means of the fuse link securing screws 6 and 1 which are threaded into suitable tapped holes in the inner ends of the knife blade terminals 4 and 5 and into corresponding tapped holes in the ends of the bar 8. Between the inner end of the blade terminal and the bar, is an arched spacer 9. The bar 8 may further be held in position by U- shaped clips l0 extendingaround the bottom of the bar and engaging .projections on the sides of the inner portions of the knife blade terminals. The ferrule 3 has an opening in its end through which the terminal 5 can be passed. A washer Il which is preferably rather loosely mounted ony the inner end of the terminal 6 is arranged to abut the end opening in the ferrule 3 and thereby 5 claims. (ci. zoo-131) to seal that end of the fuse cartridge while at the same time providing a suitable vent for gases developed when the fuse blows. If desired, the washer ll may be tensioned against a shoulder formed on the blade 5 by means of a spring washer I2 and a rigid washer I3. The other end of the fuse cartridge is closed by means of a cap I4 threaded over the ferrule 2. The cap I4 is provided with an inwardly extending flange adapted to seat a washer l5, which is fixed to the terminal 4, against the end of the ferrule 2.

A conventional form of fuse link is shown at I6.

This link comprises a metal strip of appropriate The fuse link is customarily provided with notched ends adapted to fit around the securing screws 6. In accordance with usual practice, the fuse link I6 is mounted with one face in contact with the inner ends of the knife blade terminals 4 and 5. The outer face of the link is in contact with the bottom surface of a washer positioned beneath the heads of the screws 6 and 1. Heretofore, an ordinary at washer has been used. The construction so far described is essentially the same as that described and claimed in my copending application Serial No. 648,764 filed February 19, 1946, and assigned to the same assignee as the present application.

According to my present invention, however, I provide washers I1 which are cup-shaped4 as shown in the sectional view of Fig. 2. These washers may be made of any suitable conducting material, for example of brass. The bottom of my washer is fiat lto provide an adequate bearing surface against the link I6 to hold the link yfirmly in contact with the knife blade terminals when the screw 6 is tightened. The outer surface iiares outwardly and upwardly at an acute angle. Preferably the cup wall extends upwards, conically, at an angle of approximately 45, and thence continues upwards cylindrically. The cylindrical portion of the washer cup wall preferably has a diameter substantially equal to or slightly greater than the width of the terminal within the casing, and the link securing screw is positioned with its center substantially equi-distant from the sides and the end of the terminal. In other words, the projection of the maximum washer diameter upon the terminal is a circle which preferably is at least tangent to the sides and end of the terminal or may overhang the terminal slightly. The inner surface of the washers may have a shape similar to that of the outer surface. The heads of the screws 6 and 'l preferably have a diameter equal to that of the inner, fiat, bottom portion of the washers. V By means of this washer, my expressed objects have been attained. With the flat washers heretofore used it is often necessary to invert the fuse link holding assembly to cause the washer to fall away from the surface of the terminal a suflicient distance to receive the new link. The inclined outer edge of my cupped washer facilitates installation ofa new fuse link since merely pressing the edge of the link against the washer automatically v because the screw head nts down into the cup of the washer and is consequently fully protected against such arcing.

Moreover, my washer is designed to act as an arcing tip; that is, by reason of the overhang of the washer cup beyond the link` contact surface, an arc occurring during blowing of the fuse tends to jump to the washer. Thereby, the joint v between the washer and the portion of the fuse link beneath it is protected from the excessive heat of the arc whereby a weld between the washer, the fuse link, and the knife terminal is less likely to occur. Furthermore, the arcing tip is renewable. If the outer edge of the washer has become pitted by an arc, it is only necessary, when the link is being replaced, to rotate the washer slightly to present a new edge surface or arcing tip to the arc which may occur upon the next blowing of the fuse.

In spite of the protection afforded by the arcing tip action of my washer, it may still happen, due to a severe short circuit, that melted parts of the fuse link weld the washer and terminal together so that they must be separated with considerable force. With the fiat washers heretofore used this can be accomplished only with difficulty. With my cupped washer, however, leverage can readily be obtained with ascrew driver acting between the blade terminal and the inclined surface of the washer to loosen the washer.

It will also be evident that my cup-shaped washer provides an additional advantage in that a slipping of the screw driver -out of the screw slot with a possible resulting injury to the person renewing the fuse link is substantially prevented by reason of the fact that the screw driver blade is conned within the cup of the washer.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a renewable fuse having a fuse link assembly removably mounted within a housing and including spaced terminal members at each end of the housing, a renewable fuse link connecting said terminal members and a link securing screw, the combination therewith of a washer having a portion positioned between the head of the screw and the fuse link and comprising a cupshaped member adapted to receive the head, of the screw and having a central opening at the bottom adapted to receive the shank of the screw and the remaining portions of the inner and outer surfaces of the bottom of the washer being substantially at, the wall of the cup extending upwardly and outwardly from the bottom in a conical surface inclined at an acute angle to the bottom.

2. In a renewable fuse having a fuse link assembly removably mounted within a housing and including spaced terminal members at each end of the housing, a renewable fuse link connecting said terminal members and a link securing screw, the combination therewith of a washer having a portion positioned between the head of the screw and the fuse link and comprising a cupshaped member adapted to receive the head of the screw and having a central opening at the bottom adapted to receive the shank of the screw and the remaining portions of the inner and outer surfaces of the bottom of the washer being substantially nat, the wall of the cup extending upwardly and outwardly from the bottom in a conical surface inclined at an acute angle to the bottom and terminating in an outer substantially cylindrical rim.

3. In a renewable fuse having a fuse link assembly removably mounted within a housing and including spaced terminal members at each end of the housing, a renewable fuse link connecting said terminal members and a link securing screw, the combination therewith of a washer having a portion' positioned between the head of the screw and the fuse link 'and comprising a cup-shaped member having flat bottom surface and a wall flaring outwardly from the bottom at an acute angle to the bottom and being thereby adapted to act as an arcing tip.

4. In a renewable fuse having a fuse link assembly removably mounted within a housing and including spaced terminal members ateach end of the housing and a renewable fuse link connecting said terminal members, the combination therewith of a link securing screw and a washer having a portion positioned between the head of the screw and the fuse link, said washer comprising a cup-shaped member forming a recess, the head of the screw being positioned within said recess, the thickness of the screw head being less than the height of the cup, and said member having a substantially fiat bottom surface and a wall flaring outwardly therefrom at an acute angle, the rim of said wall being thereby adapted to act as an arcing tip and to protect the hea y of the screw.

5. In a renewable fuse having a fuse.link assembly removably mounted within a housing and including spaced terminal members having'fuse link contacting surfaces at each end of the housing and a renewable fuse link connecting said terminal members, the combination therewith of a link securing screw threaded into each of said members substantially equidistantly from its sides and end and a cup-shaped washer having a portion positioned between the head of the screw and the fuse link and having an outwardly and upwardly aring wall forming a recess within which the head of the screw is positioned and having its greatest diameter not substantially less than the width of said terminal member, a portion of said wall being thereby adapted to act as an arcing tip and to protect the head of the screw.

FRED G. von HOORN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,109,733 Young Sept. 8, 1914 1,919,273 Conant July 25, 1933 2,079,097 Wood May 4, 1937 2,219,423 Kurtz Oct. 29, 1940 

